LP8754 datasheet(39/52 Pages) TI2

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LP8754

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SNVS861A – FEBRUARY 2014 – REVISED AUGUST 2014

Table 8. Suggested Input/Output Capacitors (X5R Dielectric)

MANUFACTURER

PART NUMBER

VALUE

CASE SIZE

VOLTAGE RATING

Murata

GRM188R60J106ME84

10 µF (20%)

0603

6.3 V

TDK

C1608X5R1A106KT

10 µF (10%)

0603

10 V

Taiyo Yuden

LMK107BJ106MALTD

10 µF (20%)

0603

10 V

Samsung

CL10A226MP8NUNE

22 µF (20%)

0603

10 V

Samsung

CL03A105MQ3CSNH

1 µF (20%)

0201

6.3 V

8.2.2.3 Output Capacitor Selection

Use ceramic capacitor, X7R or X5R types; do not use Y5V. DC bias voltage characteristics of ceramic capacitors

must be considered. DC bias characteristics vary from manufacturer to manufacturer, and DC bias curves should

be requested from them as part of the capacitor selection process. The output filter capacitor smooths out current

flow from the inductor to the load, helps maintain a steady output voltage during transient load changes and

reduces output voltage ripple. These capacitors must be selected with sufficient capacitance and sufficiently low

ESR to perform these functions. Minimum effective output capacitance to ensure good performance in 6-phase

configuration is 30 µF at the output voltage DC bias including tolerances and over ambient temp range.

The output voltage ripple is caused by the charging and discharging of the output capacitor and also due to its

RESR. The RESR is frequency dependent (as well as temperature dependent); make sure the value used for

selection process is at the switching frequency of the part. See suggested capacitors in Table 8.

A higher output capacitance improves the load step behavior and reduces the output voltage ripple as well as

decreasing the PFM switching frequency. For most 6-phase applications 4 x 22 µF 0603 capacitors for COUT is

suitable. Although the converter's loop compensation can be programmed to adapt to virtually several hundreds

of microfarads COUT, an effective COUT less than 120 µF is preferred -- there is not necessarily any benefit to

having a COUT higher than 120 µF. Note that the output capacitor may be the limiting factor in the output voltage

ramp, especially for very large (> 100 µF) output capacitors. For large output capacitors, the output voltage might

be slower than the programmed ramp rate at voltage transitions, because of the higher energy stored on the

output capacitance. Also at start-up, the time required to charge the output capacitor to target value might be

longer. At shutdown, if the output capacitor is discharged by the internal discharge resistor, more time is required

to settle VOUT down as a consequence of the increased time constant.

8.2.2.4 LDO Capacitor Selection

A ceramic low ESR 1.0-

μF capacitor should be connected between the VLDO and GNDA pins

8.2.2.5 VIOSYS Capacitor Selection

Adding a ceramic low ESR 1.0-

μF capacitor between the VIOSYS pin and GND is recommended. If VVIOSYS

signal is low noisy the capacitor is not required.

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